The Preparation Of Hierarchical Beta Zeolite And Its Shaping

Hierarchical zeolites have both microporous,mesoporous or macroporous structures,so that they can improve diffusion performance and the utilization efficiency of active centers,and have unparalleled advantages in catalytic reactions involving macromolecular substances.However,before the powder zeolites are put into an industrial reactor（fluidized bed,fixed bed,moving bed,slurry bed,etc.）,it must be mixed with additives such as binders and pore formers aimed to obtain necessary mechanical strength and shape matching for the form of the device.Unfortunately,the binders can reduce the acidity of the zeolites and block the pores resulting in the decrease of the specific surface area and the accessibility of the acid centers,which ultimately lead to the decrease of the catalyst performance.At present,reports on the preparation of technical Beta zeolite with full crystallization only have solved the problem of pore blocking by binders,and lack of research on acidity and hierarchical porosity.Therefore,we took the powder Beta zeolites as the parent,and systematically studied（1）the synthesis routes of hierarchical Beta zeolites;（2）the shaping process of hierarchical Beta zeolites;（3）the powder Beta zeolites firstly are mixed with Si O₂binder and then are treated by TEAOH in order to obtain technical Beta zeolite with full crystallization and recovered acidity after desilicication-recrystallization process;（4）the powder Beta zeolites firstly are mixed with Al₂O₃and then are treated by TEAOH in order to obtain technical Beta zeolite with full crystallization and recovered acidity after desilicication-recrystallization process and silicon supplementation treatment.In terms of comprehensive analysis of various characterization results and DFT theoretical calculation results,the study found that:（1）compared with the traditional alkali treatment,the treatment method of adding TEAOH for desiliconization and recrystallization can more efficiently prepare acid-recovered hierarchical Beta zeolites.However,after the above-mentioned obtained hierarchical Beta zeolites mixed with the binders for shaping,the original micropore and the mesopores obtained from the post-treatment are blocked by the binders;（2）treating the Si O₂-based technical Beta zeolite by TEAOH can obtain technical Beta zeolite with full crystallization and recovered acidity after desilicication-recrystallization process.As the results shown,the TEAOH has the dual functions of desiliconization and recrystallization,so it can effectively generate mesopores and restore acidity while achieving complete conversion of the binders.Benefiting from the restored acidity and hierarchical porosity,the n-hexane conversion of the technical catalyst samples after treatment is close to that of the parent powder,and surprisingly,the selectivity to light olefins in the high temperature region exceed that of the parent powder;（3）as for the technical Al₂O₃-based Beta,the results show that TEAOH can only play the role of alkali desilication and cannot transform the binders into the zeolite phase,but it can still promote the redistribution of Si and Al species contributing to the improve of the acidity;additional Si source can increase the degree of recrystallization,promote the Al₂O₃transformed into the zeolite phase and further increase the acidity of the zeolite.It’s worth noting that the conversion of n-hexane over catalyst sample after treatment by TEAOH and additional Si source in the low temperature region（350℃-500℃）is as high as 75%,and the yield to light olefins is as high as 32%,exceeding that of the parent Beta zeolite powder;（4）the binder type can strongly influence the physicochemical properties of the technical zeolites.